E-mail sending Problem

I am having a problem with 1 user in my company who is getting the following message when sending to one Client:

"The message could not be delivered because the recipient's destination email system is unknown or invalid. Please check the address and try again, or contact your system administrator to verify connectivity to the email system of the recipient"

I have tested sending a message to this user and it delivers and confirms that it has reached the server.

When I took a look at his reciopents in outlook I noticed that in message type (see attached file) the properties are set to mailto where as mine and all his other contacts are set to smtp.

We are using Exchange 2003 with outlook 2007.

Any thoughts on this? I must admit I have never noticed the mailto before.

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The point is that we get loads of Google Monkeys that don't know the first thing about Exchange and simply Google for something relevant and post nothing more than a "Check this out" comment and a link.

If you want to stand out from the other Experts and not get tagged as a Google Monkey, please post information from your own knowledge and back it up with a link. We all know how to Google - but we don't all know how Exchange works.

"The message could not be delivered because the recipient's destination email system is unknown or invalid. Please check the address and try again, or contact your system administrator to verify connectivity to the email system of the recipient"

As per your above posted message I understood that the receipient id is invalid
1. Please check the id twice saved in particular user local contacts and in cache
2. Remove apostrophe symbol ( ' ) or any other symbol on both side of receipient email id in TO/CC/BCC column
3. Now try sending probably it should work.

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In this video we show how to create a mailbox database in Exchange 2013. We show this process by using the Exchange Admin Center.
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